Just because the fork is moving doesnt mean that everything is good hydraulically. Check to make sure your clutch is completely bled out, i have had that issue on my 88. pop the cap on the clutch fluid reservoir, then go underneath with a ten mm wrench and crack open the bleeder screw on the slave cylinder. ( you can actually reach it pretty easily with the car on the ground and laying on your back as long as you have stock springs.) open it up with something under it to catch the fluid. let it sit there and piss out while topping of the reservoir every few seconds to keep it from going too low. after about 2 minutes close it off. pump your pedal three or four times, then open it up and repeat. Afterward make sure your fluid is topped off and the bleeder screw is tight, then fire her up and see if that helped. If not let me know.